[lproven]

The 3rd Hitchhiker novel, "Life, the Universe, and Everything", is also a repurposed Dr Who script: "Dr Who and the Krikkitmen".

[dcminter]

Heh, which reminds me, it's my head-canon that the sofa in LtU&E is the same one that's in Dirk Gently and in City of Death. Given that it's flotsam in the space time continuum it seems perfectly reasonable :)